Observing the First Galaxies and the Reionization Epoch

Observing the First Galaxiesand the Reionization EpochObserving the First Galaxiesand the Reionization Epoch

Steve Furlanetto

UCLA

February 5, 2008

Steve Furlanetto

UCLA

February 5, 2008

OutlineOutline

Introduction: Observing Reionization Galaxy Surveys

Current observations of LAEs The Clustering Signature

The 21 cm Transition as a Cosmological Probe Basic Physics The Mean 21 cm Background Measurements and Challenges The Pre-reionization IGM Reionization

Conclusion

Introduction: Observing Reionization Galaxy Surveys

Current observations of LAEs The Clustering Signature

The 21 cm Transition as a Cosmological Probe Basic Physics The Mean 21 cm Background Measurements and Challenges The Pre-reionization IGM Reionization

Conclusion

A Brief History of the UniverseA Brief History of the Universe

Last scattering: z=1089, t=379,000 yr

Today: z=0, t=13.7 Gyr

Reionization: z=6-20, t=0.2-1 Gyr

First galaxies: ?

Last scattering: z=1089, t=379,000 yr

Today: z=0, t=13.7 Gyr

Reionization: z=6-20, t=0.2-1 Gyr

First galaxies: ?

Big Bang

Last ScatteringDark Ages

Galaxies, Clusters, etc.

Reionization

G. Djorgovski

First Galaxies

ReionizationReionization

First stars and galaxies produce ionizing photons

Ionized bubbles grow and merge

Affects all baryons in the universe

Phase transition




Phase transition

Mesinger & FurlanettoMesinger & Furlanetto

ReionizationReionization





Phase transition




Phase transition

Reionization:Observational Constraints

Reionization:Observational Constraints

Quasars/GRBs CMB optical depth Ly-selected galaxies

Quasars/GRBs CMB optical depth Ly-selected galaxies

Furlanetto, Oh, & Briggs (2006)

Ly Emitters and HII RegionsLy Emitters and HII Regions

Total optical depth in Ly transition:

Damping wings are strong

Total optical depth in Ly transition:

Damping wings are strong

IGM HI

€

τGP ≈ 3x105 xHI

1+ z

7

⎛

⎝ ⎜

⎞

⎠ ⎟3 / 2

LAEs During ReionizationLAEs During Reionization

z=9, R=125 observation, with M>1.7x1010 Msun Galaxies in small bubbles (underdense regions) masked

out by absorption

z=9, R=125 observation, with M>1.7x1010 Msun Galaxies in small bubbles (underdense regions) masked

out by absorption

xH=0 xH=0.26 xH=0.51 xH=0.77

Mesinger & Furlanetto (2007)Mesinger & Furlanetto (2007)

A Declining Number Density?A Declining Number Density?

Largest survey to date with Subaru

Apparent decline at bright end

Disputed by Dawson et al. (2007)

Largest survey to date with Subaru

Apparent decline at bright end

Disputed by Dawson et al. (2007)

Kashikawa et al. (2006)

A Declining Number Density?A Declining Number Density?

Similar behavior to z=7 One (!) detection L>1043 erg/s

detection threshold

Similar behavior to z=7 One (!) detection L>1043 erg/s

detection threshold

Iye et al. (2006)

An Increasing Number Density?An Increasing Number Density?

Stark et al. (2007) found 6 candidate LAEs behind massive clusters Search along lensing caustics z=9-10 L~1041-1042 erg/s Most obvious interlopers ruled

out

Stark et al. (2007) found 6 candidate LAEs behind massive clusters Search along lensing caustics z=9-10 L~1041-1042 erg/s Most obvious interlopers ruled

out

Kashikawa et al. (2006)

Stark et al. (2007), z=9

An Increasing Number Density?An Increasing Number Density?

Solid curves show mass functions with absorption

Four scenarios for luminosities (right to left): Same as z=6 LAEs Same as z=6 LAEs, but Pop III All baryons form Pop II stars,

simultaneously All baryons form Pop III stars,

simultaneously

Reasonable scenarios require fully ionized!

Solid curves show mass functions with absorption

Four scenarios for luminosities (right to left): Same as z=6 LAEs Same as z=6 LAEs, but Pop III All baryons form Pop II stars,

simultaneously All baryons form Pop III stars,

simultaneously

Reasonable scenarios require fully ionized!

Mesinger & Furlanetto (2008)

LAE ClusteringDuring Reionization


Nearly randomly distributed galaxy population

Small bubble: too much extinction, disappears

Large bubble: galaxies visible to survey

Nearly randomly distributed galaxy population







Absorption selects large bubbles, which tend to surround clumps of galaxies



Absorption selects large bubbles, which tend to surround clumps of galaxies

Enhanced Clustering During Reionization

Enhanced Clustering During Reionization

Shows enhanced probability to have N>1 galaxies in an occupied cell

Measuring requires deep survey over ~106-107 Mpc3

Shows enhanced probability to have N>1 galaxies in an occupied cell

Measuring requires deep survey over ~106-107 Mpc3


The Future of LAE SurveysThe Future of LAE Surveys

Advantages: Familiar strategies Study galaxies as

well

Advantages: Familiar strategies Study galaxies as

well

Disadvantages: Uncertainties about

galaxy formation Need large volume,

deep surveys Indirect information

about IGM

Disadvantages: Uncertainties about

galaxy formation Need large volume,

deep surveys Indirect information

about IGM

The Spin-Flip TransitionThe Spin-Flip Transition

Proton and electron both have spin magnetic fields

Produces 21 cm radiation (=1420 MHz)

Extremely weak transition Mean lifetime ~107 yr Optical depth ~1% in fully

neutral IGM

Proton and electron both have spin magnetic fields

Produces 21 cm radiation (=1420 MHz)

Extremely weak transition Mean lifetime ~107 yr Optical depth ~1% in fully

neutral IGM

The 21 cm TransitionThe 21 cm Transition

Map emission (or absorption) from IGM gas Requires no background

sources Spectral line: measure

entire history Direct measurement of

IGM properties No saturation!

Map emission (or absorption) from IGM gas Requires no background

sources Spectral line: measure

entire history Direct measurement of

IGM properties No saturation!

SF, AS, LH (2004)

€

δTb ≈ 23xHI (1+ δ) 1+ z

10

⎛

⎝ ⎜

⎞

⎠ ⎟

1/ 2 TS −TbkgdTS

⎛

⎝ ⎜

⎞

⎠ ⎟H(z) /(1+ z)

∂vr /∂r

⎛

⎝ ⎜

⎞

⎠ ⎟ mK

€

δTb ≈ 23xHI (1+ δ) 1+ z

10

⎛

⎝ ⎜

⎞

⎠ ⎟

1/ 2 TS −TbkgdTS

⎛

⎝ ⎜

⎞

⎠ ⎟H(z) /(1+ z)

∂vr /∂r

⎛

⎝ ⎜

⎞

⎠ ⎟ mK

The Spin TemperatureThe Spin Temperature

CMB photons drive toward invisibility: TS=TCMB

Collisions couple TS to TK Dominated by electron exchange in H-H

collisions in neutral medium (Zygelman 2005) Dominated by H-e- collisions in partially

ionized medium (Furlanetto & Furlanetto 2006), with some contribution from H-p collisions (Furlanetto & Furlanetto 2007)

CMB photons drive toward invisibility: TS=TCMB

Collisions couple TS to TK Dominated by electron exchange in H-H

collisions in neutral medium (Zygelman 2005) Dominated by H-e- collisions in partially

ionized medium (Furlanetto & Furlanetto 2006), with some contribution from H-p collisions (Furlanetto & Furlanetto 2007)

The Global Signal:The Dark Ages

The Global Signal:The Dark Ages

Straightforward physics Expanding gas Recombination Compton scattering

Straightforward physics Expanding gas Recombination Compton scattering

SF, PO, FB (2006)

The Wouthuysen-Field Mechanism I

The Wouthuysen-Field Mechanism I

0S1/2

1S1/2

0P1/2

1P1/2

1P3/2

2P3/2

Selection Rules: F=0,1 (except F=0 F=0)

Mechanism is effective with ~0.1 Ly photon/baryon

The Wouthuysen-FieldMechanism II

The Wouthuysen-FieldMechanism II

Relevant photons are continuum photons that redshift into the Ly resonance

Relevant photons are continuum photons that redshift into the Ly resonance

Ly

…

LyδLyLy

The Global Signal:First Light


First stars (quasars?) flood Universe with photons W-F effect Trigger absorption in

cold IGM

First stars (quasars?) flood Universe with photons W-F effect Trigger absorption in

cold IGM

Pop II Stars

SF (2006)

feedback

Pop III Stars

The First Sources of Light:X-ray Heating

The First Sources of Light:X-ray Heating

X-rays are highly penetrating in IGM Mean free path >Mpc Deposit energy as heat,

ionization Produced by…

Supernovae Stellar mass black holes Quasars Very massive stars

X-rays are highly penetrating in IGM Mean free path >Mpc Deposit energy as heat,

ionization Produced by…

Supernovae Stellar mass black holes Quasars Very massive stars



First stars (quasars?) flood Universe with photons W-F effect Heating Ionization Timing depends on f*,

fesc, fX, stellar population

First stars (quasars?) flood Universe with photons W-F effect Heating Ionization Timing depends on f*,

fesc, fX, stellar population

Pop II Stars

SF (2006)

feedback

Pop III Stars

21 cm Observations21 cm Observations

Experiments Global Signal: CoRE-

ATNF, EDGES Fluctuations: 21CMA,

LOFAR, MWA, GMRT, PAPER, SKA

Imaging: SKA

Experiments Global Signal: CoRE-

ATNF, EDGES Fluctuations: 21CMA,

LOFAR, MWA, GMRT, PAPER, SKA

Imaging: SKA

MWAMWA

Terrestrial InterferenceTerrestrial Interference

Mileura spectrum, 15 sec integrations Two types:

Fixed site (low frequency filling factor) Aircraft/meteor trail reflections (low duty cycle)

Basic strategy: excise contaminated channels

Mileura spectrum, 15 sec integrations Two types:

Fixed site (low frequency filling factor) Aircraft/meteor trail reflections (low duty cycle)

Basic strategy: excise contaminated channels

BowmanBowman

et al. (2007)et al. (2007)

Ionospheric DistortionsIonospheric Distortions

Refraction in ionosphere distorts wavefronts

Analog of optical seeing layer

Solved on software level with calibration sources

Challenge: wide-field imaging

Refraction in ionosphere distorts wavefronts

Analog of optical seeing layer

Solved on software level with calibration sources

Challenge: wide-field imaging

W. CottonW. Cotton

Astronomical ForegroundsAstronomical Foregrounds

Landecker et al. (1969)Landecker et al. (1969) Map at 150 MHz

Contours are in Kelvin

The Synchrotron ForegroundsThe Synchrotron Foregrounds

A single synchrotron electron produces a broad but smooth spectrum


FrequencyFrequency

IntensityIntensity

B

e- path



Electron velocity scales the spectrum


Electron velocity scales the spectrum

FrequencyFrequency

IntensityIntensity


Synchrotron spectrum mirrors distribution of fast electrons

Typically near power-law, with ~K/MHz gradient

Synchrotron spectrum mirrors distribution of fast electrons

Typically near power-law, with ~K/MHz gradient

FrequencyFrequency

IntensityIntensity

Measuring the Global Signal?Measuring the Global Signal?

Signal gradient is few mK/MHz

Foregrounds vary as (near) power law Synchrotron, free-free Gradient is few K/MHz

CoRE-ATNF, EDGES experiments are trying Distinctive shape may help

Signal gradient is few mK/MHz

Foregrounds vary as (near) power law Synchrotron, free-free Gradient is few K/MHz

CoRE-ATNF, EDGES experiments are trying Distinctive shape may help

SF (2006)

Foregrounds on Small ScalesForegrounds on Small Scales

0.5 MHz

Foreground RemovalForeground Removal

Removal algorithms fairly well-developed Zaldarriaga et al. (2004), Morales & Hewitt (2004), Santos et al. (2005), McQuinn et al. (2007)

Removal algorithms fairly well-developed Zaldarriaga et al. (2004), Morales & Hewitt (2004), Santos et al. (2005), McQuinn et al. (2007)

Frequency

Tb

Cleaned Signal ~ 10 mK

Total Signal ~ 400 K

Foreground NoiseForeground Noise

Thermal noise is NOT smooth: varies between each channel

For first generation instruments, 1000 hr observations still have S/N<1 per pixel

Imaging is not possible until SKA!

Thermal noise is NOT smooth: varies between each channel

For first generation instruments, 1000 hr observations still have S/N<1 per pixel

Imaging is not possible until SKA!

The Murchison Widefield ArrayThe Murchison Widefield Array

Low Frequency Demonstrator under construction (fully funded, first light ~2008)

Located on sheep ranch in Western Australia

Low Frequency Demonstrator under construction (fully funded, first light ~2008)

Located on sheep ranch in Western AustraliaBowman et al. (2007)Bowman et al. (2007)

The Murchison Widefield ArrayThe Murchison Widefield Array

Bowtie antennae grouped in tiles of 16 Broad frequency response Large field of view

Bowtie antennae grouped in tiles of 16 Broad frequency response Large field of view

Bowman et al. (2007)Bowman et al. (2007)

Murchison Widefield Array:Low Frequency Demonstrator

Murchison Widefield Array:Low Frequency Demonstrator

Instrument characteristics Radio-quiet site 500 16-element antennae in

1.5 km distribution 7000 m2 total collecting area Full cross-correlation of all 500

antennae 80-300 MHz 32 MHz instantaneous

bandwidth at 8 kHz resolution 20-30 degree field of view

Instrument characteristics Radio-quiet site 500 16-element antennae in

1.5 km distribution 7000 m2 total collecting area Full cross-correlation of all 500

antennae 80-300 MHz 32 MHz instantaneous

bandwidth at 8 kHz resolution 20-30 degree field of view Bowman et al. (2007)Bowman et al. (2007)

Error Estimates: z=8Error Estimates: z=8

Survey parameters z=8 Tsys=440 K

tint=1000 hr B=6 MHz No systematics!

MWA (solid black) Aeff=7000 m2

1.5 km core SKA (dotted blue)

Aeff=1 km2

5 km core LOFAR very close to MWA

Survey parameters z=8 Tsys=440 K

tint=1000 hr B=6 MHz No systematics!



Aeff=1 km2

5 km core LOFAR very close to MWA

MWA

SKA

Foreground

limit

(Mpc-1)

Error Estimates: z=12Error Estimates: z=12

Survey parameters z=12 Tsys=1000 K tint=1000 hr B=6 MHz No systematics!



Aeff=1 km2

5 km core

Survey parameters z=12 Tsys=1000 K tint=1000 hr B=6 MHz No systematics!



Aeff=1 km2

5 km core

MWA

SKA

Foreground

limit

(Mpc-1)

That’s a whole lotta trouble…

So what good is it, really?

That’s a whole lotta trouble…

So what good is it, really?

The Global SignalThe Global Signal

Four Phases Dark Ages First Stars First Black Holes Reionization

Four Phases Dark Ages First Stars First Black Holes Reionization

SF (2006)

Reionization BHs Stars Dark Ages

Ly FluctuationsLy Fluctuations

Ly photons decrease TS near sources (Barkana & Loeb 2004) Clustering 1/r2 flux

Strong absorption near dense gas, weak absorption in voids

Ly photons decrease TS near sources (Barkana & Loeb 2004) Clustering 1/r2 flux


Cold, Absorbing

Cold, invisible

Ly FluctuationsLy Fluctuations

Ly photons decrease TS near sources Clustering 1/r2 flux


Eventually saturates when IGM coupled everywhere

Ly photons decrease TS near sources Clustering 1/r2 flux


Eventually saturates when IGM coupled everywhere

Cold, Absorbing

The Pre-Reionization EraThe Pre-Reionization Era

Thick lines: Pop II model, zr=7

Thin lines: Pop III model, zr=7

Dashed: Ly fluctuations

Dotted: Heating fluctuations

Solid: Net signal





Solid: Net signal

Ly

X-ray

Net

Pritchard & Furlanetto (2007)

X-ray FluctuationsX-ray Fluctuations

X-ray photons increase TK near sources (Pritchard & Furlanetto 2007) Clustering 1/r2 flux

Hot IGM near dense gas, cool IGM near voids

X-ray photons increase TK near sources (Pritchard & Furlanetto 2007) Clustering 1/r2 flux

Hot IGM near dense gas, cool IGM near voids

Hot

Cool

X-ray and Ly FluctuationsX-ray and Ly Fluctuations

+ =Hot,

emitting

Invisible






Solid: Net signal





Solid: Net signal

Ly

X-ray

Net



+ =Hot,

emitting

Cold, absorbing






Solid: Net signal





Solid: Net signal

Ly

X-ray

Net



+ =

Hot, emitting






Solid: Net signal





Solid: Net signal

Ly

X-ray

Net


21 cm Observations: Reionization

21 cm Observations: Reionization


100 Mpc comoving100 Mpc comoving

Reionization “Simulations”Reionization “Simulations”

Implement in numerical simulation boxes

Step 1: Generate initial conditions

Step 2: Identify galaxies






Biased Galaxy Formation:Peaks and Patches

Biased Galaxy Formation:Peaks and Patches

Galaxies form at peaks in the density field

Threshold decreases with time More galaxies Bigger galaxies

Galaxies form at peaks in the density field

Threshold decreases with time More galaxies Bigger galaxies

Identifying GalaxiesIdentifying Galaxies

Filter density field to find peaks

Use excursion-set barrier to find masses

Adjust locations using Zeldovich approximation

Similar to “peak-patch” method (Bond & Myers 1996), PINOCCHIO, PTHALOS

Filter density field to find peaks

Use excursion-set barrier to find masses

Adjust locations using Zeldovich approximation

Similar to “peak-patch” method (Bond & Myers 1996), PINOCCHIO, PTHALOS


Identifying GalaxiesIdentifying Galaxies

Excellent statistical agreement Large-scale structure Poisson noise

Accurate one-to-one for large galaxies (Bond & Myers 1996)

Excellent statistical agreement Large-scale structure Poisson noise

Accurate one-to-one for large galaxies (Bond & Myers 1996)


Photon CountingPhoton Counting

Assume galaxies have fixed ionizing efficiency

Isolated galaxies generate HII regions

Clustered galaxies work together




Neutral IGM

Ionized IGM

Galaxy

Photon CountingPhoton Counting









z=9.75, xz=9.75, xii=0.2=0.2




Step 2: Identify galaxies Step 3: Paint on bubbles,

working from outside in







z=8.75, xz=8.75, xii=0.4=0.4




















z=8, xz=8, xii=0.6=0.6






working from outside in Five hours on desktop!




working from outside in Five hours on desktop!


z=7.25, xz=7.25, xii=0.8=0.8


Zahn et al. (2007), Mesinger & Furlanetto (2007)Zahn et al. (2007), Mesinger & Furlanetto (2007)

Success!Success!

Excellent match for large scale features Map details depend on filtering algorithm

Excellent match for large scale features Map details depend on filtering algorithm

Filter A on halos from N-body simulation

Filter B on halos from N-body simulation

Radiative Transfer

Simulation

The 21 cm Power SpectrumThe 21 cm Power Spectrum

MWA

SKA

(Mpc-1)


MWA

SKA

21 cm-GalaxyCross-Correlation

21 cm-GalaxyCross-Correlation

Mesinger & FurlanettoMesinger & Furlanettoz=8, xz=8, xii=0.6=0.6

21 cm-Galaxy Cross-Correlation

21 cm-Galaxy Cross-Correlation

Key advantages Unambiguous confirmation of cosmological signal Vastly reduces difficulty of foreground cleaning

Only emission from sources in survey slice contributes

Increase sensitivity and dynamic range Helps with angular structure

Science!

Key advantages Unambiguous confirmation of cosmological signal Vastly reduces difficulty of foreground cleaning

Only emission from sources in survey slice contributes

Increase sensitivity and dynamic range Helps with angular structure

Science!

The 21 cm-GalaxyCross-CorrelationThe 21 cm-GalaxyCross-Correlation

Can be done with LAEs or LBGs

Significant advantages in 21 cm data analysis (SF & AL 2007)

Challenge: wide-field near-IR surveys JWST? JDEM? Ground-based cameras?

Can be done with LAEs or LBGs

Significant advantages in 21 cm data analysis (SF & AL 2007)

Challenge: wide-field near-IR surveys JWST? JDEM? Ground-based cameras?

Lidz, Zahn, & Furlanetto (in prep)Lidz, Zahn, & Furlanetto (in prep)

ConclusionsConclusions

LAE searches beginning to pay off Strange star formation? Robust signatures will be in clustering

The 21 cm transition offers great possibilities Pre-reionization: properties of first sources, cosmology Reionization: morphology and growth of bubbles Experimental challenges still large

Good synergy with other probes of high-z universe! Cross-correlation, Ly searches, quasars…

LAE searches beginning to pay off Strange star formation? Robust signatures will be in clustering

The 21 cm transition offers great possibilities Pre-reionization: properties of first sources, cosmology Reionization: morphology and growth of bubbles Experimental challenges still large

Good synergy with other probes of high-z universe! Cross-correlation, Ly searches, quasars…

See our Physics Reports review (Furlanetto, Oh, & Briggs 2006, astro-ph/0608032) for more information on 21 cm possibilities!

Observing the First Galaxies and the Reionization Epoch

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